1. Field of the Invention
This invention relates to the field of compound winding apparatuses and to counterbalance systems for window sashes and the like, and more particularly, to a compound counterbalance system incorporating a compound winding apparatus and comprising: biasing means for easing operation of a window sash and the like, the biasing means being movable in part at an inherently variable rate of force; a first biasing force transmission means, connected intermediately of the window sash and the like and the biasing means, for increasing the effective range of movement of the biasing means; and, a second biasing force transmission means connected intermediately of the window sash and the like and the biasing means, the second biasing force transmission means having a variable rate of operation predetermined to automatically compensate for the variability of the biasing means to provide a substantial constancy of the biasing force.
2. Prior Art
Counterbalance systems for window sashes and the like have been known for some time, particularly in conjunction with double hung window frames. The original counterbalance systems for such windows utilized sash weights hung by cables and pulleys, and running in large cavities to one or both sides of the window frames. Such counterbalance systems made such windows practical, but at the same time, were extremely energy inefficient. The large cavities in which the pulleys were disposed provided effective conduits for drafts running along and through the windows and the walls in which the windows were mounted. Such counterbalance systems did have one advantage, namely that the pull exerted by the sash weight was constant throughout the reciprocating range of movement of the window sashes.
A number of developments have impacted on the design of windows and counterbalance systems for windows, resulting in the inevitable obsolescence of the sash weight and pulley system. Technology has been developed to manufacture windows much less expensively off-site, in fully functioning assemblies. Such assemblies incorporate within their own structure the necessary counterbalance system. Cavities for sash weights to counterbalance windows are no longer even designed or otherwise provided for today. Accordingly, spring balances were incorporated into such manufactured window assemblies. Spring balances are advantageous in that their tension can be easily adjusted, whereas changing sash weights in a major undertaking. The ability to provide adjustable tension has proven especially important today, as energy conservation requirements demand that windows be very tightly sealed against drafts and that they provide substantial insulation. It is not generally appreciated by consumers at large that highly efficient weather stripping and weather seals exert large amounts of sliding friction, making windows and other systems incorporating such seals much more difficult to operate. Adjustably tensioned springs permit manufacturers to compensate for the additional tension which is necessary for a well-sealed and well-insulated window. Insulated windows require additional panes of glazing, increasing the weight of the sash. However, counterbalance systems incorporating springs have simply never worked as well as did sash weights, when windows were substantially unsealed, because such springs have inherent unconstant spring rates or gradients, that is, the amount of tension exerted by the spring changes according to the extent to which the spring is extended or relaxed.
In today's marketplace, window manufacturers are faced with two critical goals, namely achieving thermal efficiency (i.e., insulation and very low air infiltration), and at the same time, achieving low operating forces. There is a direct conflict in these two goals, as tightly-fitted, heavy window assemblies inherently generate higher operating forces due to friction and gravity. Today's counterbalance systems are simply not responsive to today's needs.
As might be expected, the prior art is replete with counterbalance systems for window sashes and the like, in what seems to be, at least initially, the widest variety of mechanical systems. A number of patent references disclose the use of spiral drums to compensate for tension changes in a spring, but in each instance, the spiral drum appears to have been mounted coaxially with and axially driven by the spring, and both the spring and the spiral drum have been disposed in a cavity above or below the window. Moreover, none of these patent references has used the spiral drums in further combination with a pulley system or other means for imparting a mechanical advantage, which in turn increases the effective range of movement of the biasing means. The following United States patents are representative of such teachings: U.S. Pat. Nos. 97,263; 1,669,990; 2,010,214; 2,453,424; 3,095,922; 3,615,065; and, 4,012,008.
Patent references have also disclosed windows utilizing side mounted springs and pulley systems, most of the pulley systems being arranged in a block and tackle arrangement to achieve a mechanical advantage. However, the systems disclosed in these references require all available space, and none incorporates a means compensating for changes in spring tension. United States patents representative of such teachings include: U.S. Pat. Nos. 2,262,990; 2,952,884; 3,046,618; 3,055,044; 4,078,336; and 4,238,907.
Certain references have also provided alternative solutions to compensation of variable spring rates in tensioning means, other than spiral drums and in other contexts. In U.S. Pat. No. 4,389,228 the sheaves of pulleys are so close together that only one diameter of rope or cable can fit there between. The effective diameter of the pulley therefore changes with each rotation as more of the cable is wound onto, or paid out from the drum. Other solutions are disclosed in the following United States patents: U.S. Pat. Nos. 2,774,119 and 3,335,455.
Compound winding apparatus and counterbalance systems for window sashes and the like, according to this invention, overcome all of the problems now plaguing prior art window assemblies. A compound counterbalance system according to this invention is the first such system which is sufficiently compact and sufficiently efficient to interconnect and utilize: (1) an axially expansible and contractible biasing means, (2) a constant rate of movement system providing a mechanical advantage, and (3) a variable rate of movement system to automatically compensate for inherent variability in the tension of the biasing means. Moreover, the biasing means itself is nevertheless easily adjustable. Finally, compound counterbalance systems according to this invention can be easily incorporated into off-site manufactured assemblies.
The term mechanical advantage, as used in the constant rate of movement system, requires some clarification to be meaningful in the context of this invention. There is a "cost" for every mechanical advantage. In the context of pulleys, as used in block and tackle assemblies, one can achieve significant mechanical advantage in raising a heavy load, but the load moves at a speed which is inversely proportional to the ratio of mechanical advantage, that is, much slower. The distance through which the load moves is also much less than the supporting cable at its driven end. In the context of gear systems, the "cost" is a rotational reduction. Where speed is more important than power, a mechanical disadvantage is preferred, as in an automobile's overdrive transmission. In the context of levers, a longer moment arm for the driven end of a lever will move a heavier load, but through a shorter distance, relative to the driven end. For this invention, a window sash or the like must move further than the expansion space available for, as an example, an axially extensible spring; considerably further.
The various mechanical advantage systems utilized in this invention enable maximum range of sash movement and, at the same time, minimum range of movement for expansion for appropriate parts of the biasing means. Nevertheless, the various embodiments maintain a mechanical advantage in stressing or extending the biasing means. Compound counterbalance systems according to this invention successfully exploit the "cost" of mechanical advantage systems without, in fact, sacrificing all of the benefits. Moreover, the variable rate of movement system, which is embodied in a compound winding apparatus and compensates for variability in the tension of the biasing means, can be embodied in small dimensions which further reduce space requirements for window sashes and in other applications.